1. Field of the Invention
The present invention relates to a process for purifying water including service water and waste water.
Though water is indispensable for maintaining human life together .with air, earth and the sun, recently, pollution of valuable water, which includes water pollution due to daily waste water and industrial waste water and the pollution of the sea due to tanker accidents, has been spreading on the earthwide scale to become a worldwide problem. In our country blessed with rich water resources, (1) pollution of underground water and sources of water supply caused by organic solvents used in industries of high technology and laundries, (2) eutrophication of lakes and rivers and pollution of sources of water supply caused by daily waste water due to synthetic detergents (surface active agents), and (3) water pollution caused by the outflow of agricultural chemicals used at golf courses, have extended over a wide range, and become a serious problem.
Besides, since a vast amount of chlorine and disinfectants are used in the treatment of service water in comparison with former times because of the pollution of sources of water, they may remain in service water, and form organochlorine compounds by reacting with organic materials in original water, and further, algae, planktons and mold occur according to the eutrophication of lakes, and therefore, city water tastes bad and pollution of it is becoming a serious problem.
2. Description of the Prior Art
As the conventional treatment of waste water, can be mentioned an activated sludge process, and this process, however, has defects that its reaction conditions about a temperature, pH, a gas atmosphere and toxicity are strict since it employs microorganisms, namely, living things, and that it can neither readily decompose nor remove the above-mentioned agricultural chemicals, organic solvents (particularly, halocarbon) and surface active agents (particularly, those with side chains) and has no effect on them.
As methods of treating such organic substances as to be hard to decompose biologically, can be mentioned activated carbon adsorption, chemical oxidation, reverse osmosis and incinerating treatment, and either of which has some problems in effects and economical points.
Typical oxidizers to be used in chemical oxidation are chlorine and ozone. Chlorine, however, has problems in respect of oxidizing power, reaction properties with an ammonium ion and residual chlorine due to excess injection, and besides, it forms trihalomethane and organochlorine compounds having carcinogenicity by reacting with organic substances contained in water to be treated. On the other hand, ozone has a defect that both the expenses of equipment and the cost of operation are very high (e.g., Takane Kitao, Ryosuke Yahashi, "Water Purification and Liquid Wastes Treatment", Vol. 8, No. 8, 35 (1976)). And further, incinerating treatment is impracticable in case of dilute solutions.
A Fenton reagent discovered by H. J. H. Fenton in 1890's is known to have a strong oxidizing power, in which ferrous salt is added into hydrogen peroxide water (H J H Fenton, "J Chem Soc." Vol 65, 899 (1894)). Hydrogen peroxide has large advantages that its price per unit of effective oxygen amount is fairly lower than that of ozone, and that it does not need expensive equipment, and hence, generally, studies upon the Fenton treatment, that is water treatment by means of a Fenton reagent, have been performed.
However, this method has defects that it is needed to use hydrogen peroxide solution having carcinogenicity, and that its reaction progresses at a slow rate, and further that it requires high acid conditions that the pH of water to be treated should be 2 to 4.